An analysis is being made of the origin and routes of translocation of Ca used in excitation-contraction coupling in smooth muscle, both vascular and non-vascular. A series of antagonists of the 1,4-dihydropyridine class is being examined for antagonism towards Ca movements through specific Ca2 ion channels. Attempts will be made to correlate Ca uptake with muscarinic receptor, Ca2 ion channel binding and guanylate cyclase activation in g.p. intestinal muscle. Ca movements in vascular tissue from normotensive and spontaneously hypertensive rats will be examined to determine the relationship of any changes to altered vascular reactivity.